Question

A bolt of lightning strikes the ground 200m from a 100 turn coil(radius of 0.8m). If the current in the lightning falls from 6.02x10^6A to zero in 10.5us, what is the average magnetic induction at the coil's position? (Treat the lightning bolt as a vertical wire, and be sure to show direction of the current in the coil. Consider only the last of the two changes as the current drops to zero.)